1. Field of the Invention
The present invention relates to a dimension measurement method, a method of manufacturing a semiconductor device, a dimension measurement apparatus and a measurement mark, and is directed, for example, to scatterometry of a shape parameter of patterns formed in a manufacturing process of a semiconductor device.
2. Description of the Related Art
A technique to measure dimensions of a pattern in a manufacturing process of a semiconductor device has heretofore been limited substantially to a technique using a measurement mark in which a one-dimensional line-and-space pattern is formed, and has not been applicable to patterns having an arbitrary shape such as a hole pattern.
A related conventional art will be described referring to FIG. 13A to FIG. 17. FIGS. 13A and 13B show one example of the line-and-space measurement mark, wherein FIG. 13A is a plan view thereof and FIG. 13B is a sectional view along the cutting-plane line L-L of FIG. 13A. For a measurement mark MK100 shown in FIGS. 13A and 13B, a thin film is formed on an upper surface of a semiconductor wafer W, and trenches TG1 to TG4 are formed through processes using photolithography, etching and the like, thus forming one-dimensional line-and-space patterns in a plan view. In the measurement mark MK100, the trenches TG1 to TG4 are provided with widths LX1 to LX4 and depths DX1 to DX4, respectively.
FIG. 14 is a block diagram showing one example of a conventional dimension measurement apparatus according to the related conventional art. A dimension measurement apparatus 100 shown therein comprises a light source 110, a polarizer 112, a stage 140, an analyzer 114, an array of detectors 116, a computer 118 and a memory MR100. The light source 110 emits white light. The stage 140 moves the wafer W through revolving movement (in a RV direction) and translational movement (in a TR direction). The detectors 116 include a spectroscope. The memory MR100 has a plurality of storage areas, and stores measurement profile charts which will be described later, and also stores several values which will be candidates for an average value LXave of the widths LX1 to LX4 of the trenches TG1 to TG4 and several values which will be candidates for an average value DXave of the depths DX1 to DX4 of the trenches TG1 to TG4.
One example of a conventional dimension measurement method using the dimension measurement apparatus 100 shown in FIG. 14 will be described.
First, the stage 140 moves the wafer W in combination of the revolving movement in the RV direction and the translational movement in the TR direction such that the white light falls on the target measurement mark MK100. In the example shown in FIG. 14, the wafer W is moved so that its notch NT is directed downward of the drawing.
Next, the white light is emitted by the light source 110, turned into incident light Li via the polarizer 112, and then caused to obliquely fall on the measurement mark MK100 at an incidence angle θ. As reflected diffracted light Lr is generated from the measurement mark MK100, this reflected diffracted light Lr is detected by the detectors 116 via the analyzer 114, and a detection signal is sent to the computer 118. The computer 118 processes this detection signal and plots a measurement profile in a graph whose horizontal axis indicates a wavelength λ and whose vertical axis indicates reflected light intensity I as indicated by a broken line ML100 in FIG. 15, which is stored by the memory MR100. The computer 118 also derives, from the memory MR100, candidate values for the average value LXave of the widths and candidate values for the average value DXave of the depths of the line-and-space trench patterns, in order to substitute these values for a predetermined theoretical model such as RCWA. The computer 118 then, as represented by a full line TL100 in FIG. 15, plots theoretical profiles in the graph whose horizontal axis indicates the wavelength λ and whose vertical axis indicates reflected light intensity I, and identifies a theoretical profile which is the most approximate to the measurement profile ML100 among the plotted theoretical profiles, and then outputs, as measurement values, the candidate value for the average value LXave of the widths and the candidate value for the average value DXave of the depths that have been input when the identified theoretical profile is calculated.
In this way, according to the conventional method, the line-and-space patterns constituting the measurement mark MK100 are used, so that diffracted light due to periodic characteristics of the one-dimensional pattern alone is generated from these patterns, and the pattern dimension can be rapidly calculated by the conventional theoretical model such as RCWA.
However, the above-mentioned conventional method has not been applicable when patterns other than the line-and-space patterns are used for the measurement mark.
For example, in cylindrical hole patterns constituting a measurement mark MK120 shown in FIGS. 16A to 16C, the values of widths and depths may differ depending on the direction of measurement, and this is because the diffracted light is generated in both an X direction and a Y direction, that is, due to two-dimensional periodic characteristics: for example, widths LHX1 to LHX8 and depths DHX1 to DHX8 in the X direction, and for example, widths LHY1 to LHY8 and depths DHY1 to DHY8 in the Y direction. Therefore, even if the candidate values for an average value LHXave of the widths in the X direction, an average value DHXave of the depths in the X direction, an average value LHYave of the widths in the Y direction and an average value DHYave of the depths in the Y direction are input into the conventional theoretical model such as the RCWA method, a candidate profile for a theoretical model TL can not be calculated rapidly.
More specifically, a two-dimensional theoretical model has to be used to enhance measurement accuracy, and in that case measurement steps, the number of which corresponds to the square of the number of steps for a one-dimensional theoretical model, are needed for the calculation thereof, which is unpractical. Moreover, if the theoretical profile is calculated within a limited amount of time, a result will be far away from the measurement profile ML120 like a theoretical profile TL120 shown in FIG. 17, leading to a problem of significantly degraded measurement accuracy.